The present invention relates generally to drug delivery, and more specifically relates to novel pharmaceutical dosage forms that provide pulsatile delivery of an antiarrhythmic agent for optimal therapeutic response. The invention additionally relates to methods for administering an antiarrhythmic agent using the novel dosage forms.
Antiarrhythmic agents are employed to treat patients suffering from, inter alia, cardiac contractions that are too rapid, too slow or asynchronous. Generally, antiarrhythmic agents are classified according to the Vaughan Williams"" classification. For example, beta adrenoreceptor-blocking agents are classified as xe2x80x9cClass IIxe2x80x9d antiarrhythmic agents and potassium channel blocking agents are classified as xe2x80x9cClass IIIxe2x80x9d antiarrhythmic agents.
Sotalol, N-[4-[1-hydroxy-2-[(1-methylethyl)amino]ethylphenyl]methane-sulfonamide, is a nonselective beta-adrenoreceptor blocking (Vaughan Williams Class II) agent with additional Class III antiarrhythmic properties, i.e., the ability to prolong the duration of the action potential. Both of these pharmacological properties contribute to the antiarrhythmic efficacy of sotalol. These same properties, however, may also cause cardiac toxicity with bradyarrhythmias, hypotension and torsade de pointes episodes, particularly with excessive doses of sotalol. Both isomers, i.e., d-and l-sotalol, have similar Class III antiarrhythmic effects, while the l-isomer is responsible for virtually all beta-blocking activity. The racemic form, i.e., dl-sotalol, has both Class III antiarrhythmic and beta-blocking activities and has been marketed as a treatment of documented ventricular arrhythmias.
Sotalol hydrochloride is currently marketed in the United States by Berlex Laboratories in 80, 120, 160 and 240 mg tablets. To reduce the risks associated with sotalol therapy, the labeling recommends that treatment should be initiated with low doses (80 mg twice daily) administered in a monitored setting followed by a gradual dose increase to 120 to 160 mg twice daily. The drug can be given parentally and is marketed for intravenous administration in several countries outside the United States.
The clinical pharmacokinetics of sotalol have been extensively studied. The drug is completely absorbed after oral ingestion on an empty stomach with time to maximum concentration occurring between about two to four hours following ingestion. When given with food, absorption is approximately 80%. After absorption, there is no significant presystemic metabolism, and the drug is completely bioavailable. Sotalol is not subject to many drug/drug interactions since sotalol exhibits negligible protein binding. The apparent volume of distribution of sotalol is two liters per kilogram of body weight. There is no major biotransformation of the drug after its absorption in the liver or other organs, and it is eliminated almost entirely (80-90%) by renal excretion as unchanged sotalol. Sotalol has a terminal elimination half-life of about 10 to 20 hours, and the drug""s pharmacokinetics are unchanged with long-term administration. The usual antiarrhythmic dose of sotalol hydrochloride is 160 to 320 mg daily given in two or three doses. The clearance of sotalol is decreased in renal insufficiency and adjustment in the dosing interval or doses becomes necessary in kidney-compromised situations. The elderly may also experience decreased elimination of sotalol due to an age-related reduction in renal clearance.
To minimize the risks associated with sotalol therapy, patients are initiated on the drug at low doses, under close supervision, while monitoring both the degree of beta-blockade as well as electrocardiac activity. This approach generally requires patients to stay in the hospital for four days during which the pharmacodynamic response is closely supervised. In this way, the physician is ensured that the patient is suitably stabilized with respect to ventricular arrhythmias or supraventricular arrhythmias such as arterial fibrillation and arterial flutter. After normal rhythm has been achieved, patients are discharged with a view to continuing treatment with twice or three times daily administration of sotalol. In order to overcome compliance problems and assist caregivers, there is a need in the art for a dosage regimen wherein the drug is administered in a convenient dosage form to these critical patients. The present invention is addressed to this need in the art by providing a means for administering an antiarrhythmic drug, e.g., sotalol, in a convenient dosage form.
It has been reported that possible loss of clinical efficacy occurs as a result of pharmacological tolerance after twice or three times daily dosing (80 mg each administration) in four out of ten patients after six days of dosing. Padrini et al. (1997) Br. J. Clin. Pharmacol. 44:463-470; Le Coz (1992) Clin. Pharmacol. Ther. 52:417-426. Therefore, for optimal response and maintenance of efficacy in a majority of patients, it is important for patients to have a drug release-free or nearly drug release-free period in order to allow the receptors to return to their basal state. Thus, in order to minimize the development of tolerance, there is a need for a delivery system to deliver sotalol in a pulsatile manner having the appropriate drug release profile.
Clearly, the development of such a pulsatile delivery release system would be more desirable than a sustained release dosage form which generally delivers an active agent in a zero order release or at a constant rate. It is important to understand that if constant plasma levels (i.e., as provided by dosage forms having a zero order release or constant rate release) are delivered (or maintained) in these patients, there is the potentially serious problem of lost clinical efficacy as a result of supra sensitization, i.e., loss of repolarization of the cardioreceptors associated with beta-blockade and potassium channel blockade. In effect, these receptors get xe2x80x9ctiredxe2x80x9d due to constant presence of the drug. Preferably, the cardioreceptors are given a period of time free from the presence of the drug so that the cardioreceptors may return to their normal state.
By providing a pulsatile delivery dosage form for administering sotalol, the invention mimics twice or three times daily dosing of sotalol. That is, the invention provides an immediate dose followed by one or more pulsatile doses several hours after ingestion of the dosage form. The pulsatile delivery dosage form of the invention improves compliance in critically ill patients and minimizes the development of tolerance. In addition, the pulsatile delivery dosage forms are ideal for controlling life-threatening arrhythmias in patients who have been discharged from clinical/hospital care.
A four-year Electrophysiologic Study vs. Electrocardiographic Monitoring (ESVEM) investigators"" trial with sotalol has demonstrated that sotalol reduces the probability of recurrent ventricular tachycardia compared with Class I agents examined in the study. Lazzara et al. (1994) Pacing Clin. Electrophysiol. 17:473-477. This trial assessed the long-term efficacy of racemic sotalol, imipramine, mexiletine, pirmenol, procainamide, propafenone and quinidine in 496 patients with histories of sustained ventricular tachyarrhythmias who were identified as responders based upon electrophysiologic testing or Holier monitoring. In the ESVEM trial, sotalol was more effective than the other agents in preventing death from arrhythmias or any other cardiac cause.
Sotalol is associated with side effects of beta-adrenergic blocking agents with a 4 to 6% incidence of proarrhythmias and a general incidence of torsade de pointes episodes. The incidence of torsade de pointes episodes associated with sotalol administration is greatest in patients with a history of sustained ventricular tachycardia. It is common that most torsade de pointes episodes occur within three days upon starting the therapy and the risk is related to the dose. This risk increases at dosages above 320 mg per day. This is probably due to the fact that sotalol blocks potassium ion conductance in a concentration-related manner: the higher the concentration, the greater the potassium channel blockade and the duration of the ventricular action potential, i.e., the QT interval. Due to this relationship, the occurrence of torsade de pointes episodes associated with sotalol administration would appear to be predictable since concentration of sotalol can be monitored and pharmacodynamic response determined before initiating long-term therapy with the drug. Sotalol-induced proarrhythmias may be explained, at least in part, by the fact that nearly any drug that delays repolarization can result in early after-depolarizations. There are small membrane oscillations that occur before full cell recovery and they have been closely linked with torsade de pointes episodes.
From the SWORD trial (survival with oral d-sotalol, Waldo et al. (1995) Am. J. Cardiol. 75(15):1023-1027; Waldo et al. (1996) Lancet 348(9019):7-12) it is important to distinguish between racemic sotalol and d-sotalol, which has the pure potassium channel blocking activity. In this study of 3,121 high-risk post-myocardial infarction patients, who had a left ventricular ejection fraction of 40% or below, administration of d-sotalol was associated with presumed proarrhythmias and resulted in increased mortality compared with placebo. Therefore, it can be postulated that the strikingly different results of the SWORD and ESVEM trials may be related to the beta-adrenergic blocking activity of racemic sotalol. Similarly, it is possible that antiadrenergic modulation of prolonged repolarization may produce a beneficial effect that exceeds that of beta-blockade alone.
It has been suggested that sotalol plasma concentration associated with beta-blockade were four- to nine-fold lower than its plasma concentration associated with significant Class III actions. Wang et. al. (1986) Am. J. Cardiol. 57:1160-1165; Nattel et al. (1989) J. Am. Coll. Cardiol. 13:1190-1194. However, other studies have shown that the concentration of sotalol associated with Class II action (beta-blockade) were similar to those associated with minimal Class III action (potassium channel blockade).
The decrease in heart rate observed during treatment with sotalol may be explained by its beta-blocking (Class II) activity. d-Sotalol, which has very low affinity (50-fold less than l-sotalol) for the beta-adrenergic receptor, also slows heart rate. However, this effect is less pronounced than racemic sotalol. A study by Funck-Brentano et al. (Funck-Brentano et al. (1990) Brit. J. of Clin. Pharmacol. 30:195-202) found that more than 99% enantiomerically pure d-sotalol, when given in tablets, decreased resting and exercise heart rate without altering blood pressure. Subsequently, it was also reported that this decrease in heart rate was not due solely to binding of d-sotalol to beta-adrenergic receptors (Ysuda et al. (1993) Clin. Pharma. and Ther. 53:436-442). These observations suggest that prolongation of the duration of the action potential in the sinus node is responsible for the effects of d-sotalol on heart rate. Thus, a Class III effect of sotalol in the sinus node may contribute to the decrease in heart rate associated with beta-blocking activity. The Class III actions of most potassium channel blockers are associated with positive inotropy. Tande et al. (1991) J. of Cardiovasc. Pharmacol. 18:687-695; Baskin et al. (1991) J. of Cardiovasc. Pharmacol. 18:406-414. This positive inotropy associated with the Class III actions of sotalol may be counterbalanced by the negative inotropic actions associated with its beta-blocking activity. Despite the fact that sotalol appears to be well tolerated in patients with impaired left ventricular ejection fraction (Singh et al. (1989) American J. of Cardiology 64:943-945), some reports indicate that sotalol has the potential to decrease ventricular contractility (Mahmarian et al. (1987) Circulation 76:324-331).
More recent studies such as the ESVEM and SWORD trials have led Bawman to postulate (Bawman (1997) Pharmacotherapy Supplement 17:768-769) that the antiadrenergic modulation of prolonged repolarization may produce a beneficial effect that exceeds that of beta-blockade alone. Therefore, both d-and l-isomers contribute to the beneficial effects of racemic sotalol in Class III antiarrhythmic efficacy. The combination of Class II and Class III actions probably gives sotalol a unique pharmacodynamic profile relative to other antiarrhythmic drugs. Recently, Ritchie et al. (Ritchie et al. (1998) J. of Cardiovasc. Pharmacol. 31:876-884) reported short-term myocardial uptake of d-and l-sotalol in humans in relation to hemodynamic and electrophysiologic effects. That study demonstrated that both the uptake and attainment of peak effects of sotalol are very rapid in humans, which are irrespective of the effect of coronary disease and in spite of the existence of content/effect/hysteresis. Ritchie et al. demonstrated that myocardial handling of sotalol is not stereoselective. This, together with the recent finding that d-sotalol induces increased mortality by arrhythmogenesis (Bawman (1997), supra), suggest that the clinical efficacy of d, l-sotalol depends critically on the maintenance of combined beta-adrenoreceptor (Class II) and potassium channel (Class III) blockade.
Thus, it appears that both isomers of sotalol are required for clinical efficacy of sotalol for treating ventricular tachyarrhythmias or arterial fibrillation or flutter. Furthermore, the pure d-sotalol isomer may find application where potassium channel blockade is required, and the l-isomer where beta-blockade is required. Although sotalol in the U.S. has been marketed for ventricular arrhythmias, the drug has found off-label use in treatment of supraventricular arrhythmias such as arterial fibrillation and arterial flutter (Pink Sheet May 3rd, 1999) and is being considered for this indication.
Le Coz et al. (1992), supra, reported that in 83% of cases, QTc (the interval of the ventricular action potential corrected for heart rate) duration during repeated oral administration of racemic sotalol was below the value predicted from single administration. Furthermore, Le Coz et al reported that in 21% of cases, the measured QTc fell outside the 95% confidence interval predicted for the QTc value. A study by Padrini et al. (Padrini et al. (1997) Br. J. Clin. Pharmacol. 44:463-470) in 10 patients evaluated the issue of tolerance to the repolarization effects of racemic sotalol during long term treatment. In this study, QT interval duration was evaluated after a single oral 160 mg sotalol dose and after 6 days multiple oral sotalol dosing (80 mg, twice daily in 9 patients and 80 mg three times daily in one patient). It was noted that QT prolongation was linearly correlated with racemic sotalol plasma concentrations. The maximum QT interval prolongation and peak plasma concentration obtained with acute and chronic drug administration were not significantly different. During maintenance treatment with sotalol, partial loss of repolarization effect occurred in four out of the ten patients, suggesting pharmacodynamic tolerance. However, in the remaining six patients no such pharmacologic tolerance was noted, suggesting that in the majority of patients, twice or three times daily dosing would be appropriate.
Therefore, delivery systems based on a pulsatile delivery approach, as provided herein, are the most desirable for critically ill patients. A delivery system of sotalol which releases the drug in such a way that a constant concentration of drug is maintained in systemic circulation will not be appropriate for therapy because there will be loss of efficacy due to pharmacodynamic tolerance. This invention addresses this and other needs in the art by providing a delivery system for administration of an antiarrhythmic agent such that an immediate release dose is followed by one or more pulsatile doses that are released hours later. One such dosage form provides pulsatile delivery of an antiarrhythmic agent that mimics a twice daily dosing regimen. Another such dosage form provides pulsatile delivery of an antiarrhythmic agent that mimics a three times a day dosing regimen.
Accordingly, it is a primary object of the invention to address the above-mentioned needs in the art by providing a pharmaceutical dosage form for pulsatile delivery of an antiarrhythmic agent. Although the active agent may be any antiarrhythmic agent, it is preferred that the agent has Class II or Ill antiarrhythmic activity. Particularly preferred Class II antiarrhythmic agents are dl-sotalol, d-sotalol, l-sotalol, pharmacologically acceptable acid addition salts thereof and mixtures of any of the foregoing. A particularly preferred Class III antiarrhythmic agent is amiodarone and pharmacologically acceptable acid addition salts thereof.
It is another object of the invention to provide a pharmaceutical dosage form that provides an initial rapid release of a therapeutically effective dose of an antiarrhythmic agent followed by so-called xe2x80x9cdelayed releasexe2x80x9d pulses such that a second and optional third delayed dose of the active agent is released from the dosage form. By incorporating both an immediate release dosage unit and one or more delayed release dosage units of the active agent, the dosage form mimics a multiple dosing profile with only a single administration. For example, the dosage form provides a twice daily dosing profile when the dosage form contains both an immediate release dosage unit and a single delayed release dosage unit. Alternatively, the dosage form provides a three times daily dosing profile when the dosage form contains an immediate release dosage unit and two delayed release dosage units. Furthermore, the dosage form provides a nearly drug release-free period of approximately 8 to 12 hours between the two doses (or xe2x80x9cpulsesxe2x80x9d) for dosage forms designed to mimic the twice daily dosing and approximately 7 to 9 hours between each of the released doses for the dosage form designed to mimic three times daily dosing.
Thus, the invention provides a pulsatile release dosage form for treating conditions responsive to the administration of an antiarrhythmic agent, wherein the dosage form comprises an immediate release dosage unit, a delayed release dosage unit and an optional second delayed release dosage unit. The immediate release dosage unit comprises a first dose of an active agent that is released substantially immediately following oral administration of the dosage form to a patient. The delayed release dosage unit comprises a second dose of the active agent and a means for delaying release of the second dose until approximately 6 hours to less than 14 hours following oral administration of the dosage form. The second delayed release dosage unit, when present, comprises a third dose of the active agent and a means for delaying release of the third dose until at least 14 hours to approximately 18 hours following oral administration of the dosage form.
Each dosage form contains a therapeutically effective amount of active agent. For dosage forms that mimic the twice daily dosing profile, approximately 30 wt. % to 70 wt. %, preferably 40 wt. % to 60 wt. %, of the total amount of active agent in the dosage form is released in the initial pulse, and, correspondingly approximately 30 wt. % to 70 wt. %, preferably 40 wt. % to 60 wt. %, of the total amount of active agent in the dosage form is released in the second pulse. For dosage forms mimicking the twice daily dosing profile, the second pulse is preferably released approximately 8 hours to less than 14 hours, and most preferably approximately 10 hours to 12 hours, following administration. For dosage forms mimicking the three times daily dosing profile, approximately 25 wt. % to 40 wt. % of the total amount of active agent in the dosage form is released in the initial pulse, and approximately 25 wt. % to 40 wt. % of the total amount of active agent in the dosage form is released in each of the second and third pulses. For dosage forms that mimic the three times daily dosing profile, release of the second pulse preferably takes place approximately 6 hours to 10 hours, and most preferably approximately 7 to 9 hours, following oral administration. Release of the third pulse occurs at least 14 hours to approximately 18 hours following oral administration in the dosage forms that mimic a three times daily dosing regimen.
There are a number of forms which the present invention may take in order to provide the desired release profile.
One form comprises a closed capsule housing at least two drug-containing dosage units. Each dosage unit may comprise a compressed tablet or plurality of compressed tablets or may comprise a plurality of beads, granules or particles, providing that each dosage unit has a different drug release profile. The immediate release dosage unit releases drug substantially immediately following oral administration to provide an initial dose. The delayed release dosage unit releases drug approximately 6 hours to less than 14 hours following oral administration to provide a second dose. Finally, an optional second delayed release dosage unit releases drug at least 14 hours to approximately 18 hours following oral administration to provide a third dose.
Another dosage form of the invention comprises a compressed tablet having a drug-containing immediate release dosage unit, a delayed release dosage unit and an optional second delayed release dosage unit, In this dosage form, the immediate release dosage unit comprises a plurality of beads, granules or particles and releases drug substantially immediately following oral administration to provide an initial dose. The delayed release dosage unit comprises coated beads or granules and releases drug approximately 6 hours to less than 14 hours following oral administration to provide a second dose. Finally, an optional second delayed release dosage unit comprises beads or granules and releases drug at least 14 hours to approximately 18 hours following oral administration to provide a third dose. The beads or granules in the delayed release dosage unit(s) are coated with a bioerodible polymeric material. This coating prevents the drug from being released until the appropriate time, i.e., approximately 6 hours to less than 14 hours following oral administration for the delayed release dosage unit and at least 14 hours to approximately 18 hours following oral administration for the optional second delayed release dosage unit. In this dosage form the components may be admixed in the tablet or may be layered to form a laminated tablet.
Another dosage form of the invention is a tablet having a drug-containing immediate release dosage unit, a delayed release dosage unit, and an optional second delayed release dosage unit, wherein the immediate release dosage unit comprises an outer layer that releases the drug substantially immediately following oral administration. The arrangement of the remaining delayed release dosage(s), however, depends upon whether the dosage form is designed to mimic twice daily dosing or three times daily dosing.
In the dosage form mimicking twice daily dosing, the delayed release dosage unit comprises an inner core that is coated with a bioerodible polymeric material. The coating is applied such that release of the drug occurs approximately 6 hours to less than 14 hours following oral administration. In this form, the outer layer completely surrounds the inner core.
In the dosage form mimicking three times a day dosing, the (first) delayed release dose comprises an internal layer that releases drug approximately 6 hours to less than 14 hours following oral administration. This internal layer is surrounded by the outer layer. The second delayed release dosage unit generally comprises an inner core that releases the drug at least 14 hours to approximately 18 hours following oral administration. Thus, the layers of this tablet (starting from the external surface) comprise an outer layer, an internal layer and an inner core. The inner core comprises delayed release beads or granules. Furthermore, the internal layer comprises the drug coated with a bioerodible polymeric material.
Alternatively, in this particular dosage form mimicking three times a day dosing, both the delayed release dosage unit and second delayed release dosage units are surrounded by an inner layer. This inner layer is free of active agent. Thus, the layers of this tablet (starting from the external surface) comprise an outer layer, inner layer and an admixture of the delayed release dosage units. The first delayed release pulse occurs once the inner layer is substantially eroded thereby releasing the admixture of the delayed release dosage units. The dose corresponding to the (first) delayed release dosage unit is released immediately since the inner layer has prevented access to this dose for the appropriate time, e.g., from approximately 6 hours to 10 hours. The second delayed release dose, however, is formulated to effectively delay release for at least 14 hours to approximately 18 hours following oral administration.
For formulations mimicking twice daily dosing, it is preferred that the delayed release dose is released approximately 8 hours to less than 14 hours, most preferably approximately 10 hours to 12 hours, following oral administration. For formulations mimicking three times daily dosing, it is preferred that the (first) delayed release dose is released approximately 6 to 10 hours, preferably 7 hours to 9 hours, following oral administration. For dosage forms containing a third dose, the third dose (i.e., the second delayed release dose) is released at least 14 hours to approximately 18 hours following oral administration.
It is another object of the invention to provide methods for administering antiarrhythmic agents, e.g., d-sotalol, l-sotalol or combinations thereof (including d,l-sotalol, i.e., racemic sotalol) and amiodarone, using the novel dosage forms.
The novel drug dosage forms are to be administered orally to a mammalian individual and can be used to administer an antiarrhythmic agent to treat or to prevent a variety of cardiovascular disorders, conditions and diseases. In accordance with the present invention, administration of the antiarrhythmic agent may be carried out in order to treat any disorder, condition or disease for which antiarrhythmic agents are generally indicated either now or in the future. Such cardiovascular conditions and diseases include, for example, documented ventricular arrhythmias, such as sustained ventricular tachycardia, that can be life threatening.
Definitions and Nomenclature
Before the present formulations and methods of use are disclosed and described, it is to be understood that unless otherwise indicated this invention is not limited to specific pharmacologically active agents, specific pharmaceutical carriers, or to particular administration regimens, as such may vary. It is also to be understood that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting.
It must be noted that, as used in the specification and the appended claims, the singular forms xe2x80x9ca,xe2x80x9d xe2x80x9canxe2x80x9d and xe2x80x9cthexe2x80x9d include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to xe2x80x9can active agentxe2x80x9d includes mixtures of active agents, reference to xe2x80x9ca pharmaceutical carrierxe2x80x9d includes combinations of two or more carriers, reference to xe2x80x9ca compressed tabletxe2x80x9d includes a plurality of compressed tablets, and the like.
In this specification and in the claims which follow, reference will be made to a number of terms which shall be defined to have the following meanings:
xe2x80x9cOptionalxe2x80x9d or xe2x80x9coptionallyxe2x80x9d means that the subsequently described circumstance may or may not occur, so that the description includes instances where the circumstance occurs and instances where it does not. For example, when an xe2x80x9coptional second delayed release dosage unitxe2x80x9d appears in describing the dosage forms, xe2x80x9coptional second delayed release dosage unit,xe2x80x9d means that the second delayed release dosage unit may or may not be present, and thus, the description includes dosage forms wherein the second delayed release dosage unit is present and dosage forms wherein the second delayed release dosage unit is not present.
The terms xe2x80x9cactive agent,xe2x80x9d xe2x80x9cdrugxe2x80x9d and xe2x80x9cpharmacologically active agentxe2x80x9d are used interchangeably herein to refer to a chemical material or compound which, when administered to an organism (human or animal, generally human) induces a desired pharmacologic effect. In the context of the present invention, the terms refer to an antiarrhythmic agent, i.e., a Class II or Class III antiarrhythmic agent, that is capable of being delivered orally. Sotalol and amiodarone are particularly preferred active agents for use in the present invention.
By the terms xe2x80x9ceffective amountxe2x80x9d or xe2x80x9cpharmaceutically effective amountxe2x80x9d of an agent as provided herein are meant a nontoxic but sufficient amount of the agent to provide the desired therapeutic effect. The exact amount required will vary from subject to subject, depending on age, general condition of the subject, the severity of the condition being treated, the particular active agent administered, and the like. Thus, it is not possible to specify an exact xe2x80x9ceffective amount.xe2x80x9d However, an appropriate xe2x80x9ceffectivexe2x80x9d amount in any individual case may be determined by one of ordinary skill in the art using routine experimentation.
By xe2x80x9cpharmaceutically acceptablexe2x80x9d carrier is meant a carrier comprised of a material that is not biologically or otherwise undesirable, i.e., the material may be administered to an individual along with the selected active agent without causing any undesirable biological effects or interacting in a deleterious manner with any of the other components of the pharmaceutical composition in which it is contained. The term xe2x80x9ccarrierxe2x80x9d is used generically herein to refer to any components present in the pharmaceutical formulations other than the active agent or agents, and thus includes diluents, binders, lubricants, disintegrants, fillers, coloring agents, wetting or emulsifying agents, pH buffering agents, preservatives, and the like.
Similarly, a xe2x80x9cpharmaceutically acceptablexe2x80x9d salt of a compound as provided herein is a salt that is not biologically or otherwise undesirable.
xe2x80x9cPulsatile Releasexe2x80x9d Dosage Forms
The active agent incorporated in the xe2x80x9cpulsatile releasexe2x80x9d of the present invention is an antiarrhythmic agent. Antiarrhythmic agents include those agents that normalize irregular electrical activity of cardiac tissue. According to the Vaughan Williams"" classification, antiarrhythmic agents are loosely classified in the following groups: Class I agents, exemplified by the sodium channel-blocking drugs; Class II agents, exemplified by beta adrenoreceptor-blocking agents; Class III agents, exemplified by drugs that prolong the effective refractory period by prolonging the action potential; and Class IV agents, exemplified by calcium channel-blocking agents.
The antiarrhythmic agent may be present in the formulation as a salt, ester, amide or other derivative, or may be functionalized in various ways as will be appreciated by those skilled in the art and described in the pertinent texts, patents and literature. The antiarrhythmic agents of the present invention can either be synthesized using techniques well known in the art or obtained from commercial suppliers.
Antiarrhythmic agents may exist in the dosage form in the form of a salt, ester, amide, prodrug, derivative or the like, provided that the salt, ester, amide, prodrug or derivative is suitable pharmacologically, i.e., effective in treating cardiac arrhythmias. Salts esters, amides, prodrugs and other derivatives of the antiarrhythmic agents may be prepared using standing procedures known to those skilled in the art of synthetic organic chemistry and described, for example, by J. March, Advanced Organic Chemistry: Reactions , Mechanisms and Structure, 4th edition. (New York: Wiley-Interscience, 1992). For example, acid addition salts are prepared from the free base using conventional methodology, and involves reaction with a suitable acid. Generally, the base form of the drug is dissolved in a polar organic solvent such as methanol or ethanol and the acid is added thereto. The resulting salt either precipitates or may be brought out of solution by addition of a less polar solvent. Suitable acids for preparing acid addition salts include both organic acids, e.g., acetic acid, propionic acid, glycolic acid, pyruvic acid, oxalic acid, malic acid, malonic acid, succinic acid, maleic acid, fumaric acid, tartaric acid, citric acid, benzoic acid, cinnamic acid, mandelic acid, methanesulfonic acid, ethanesulfonic acid, p-toluenesulfonic acid, salicylic acid, and the like, as well as inorganic acids, e.g., hydrochloric acid, hydrobromic acid, sulfuric acid, nitric acid, phosphoric acid, and the like. An acid addition salt may be reconverted to the free base by treatment with a suitable base. Particularly preferred acid addition salts of the antiarrhythmic agents herein are halide salts, such as may be prepared using hydrochloric or hydrobromic acids. Conversely, preparation of basic salts of acid moieties which may be present on the molecule of the antiarrhythmic agent are prepared in a similar manner using a pharmaceutically acceptable base such as sodium hydroxide, potassium hydroxide, ammonium hydroxide, calcium hydroxide, trimethylamine, or the like. Particularly preferred basic salts herein are alkali metal salts, e.g., sodium salt, and copper salts. Preparation of esters involves functionalization of hydroxyl and/or carboxyl groups which may be present within the molecular structure of the drug. The esters are typically acyl-substituted derivatives of free alcohol groups, i.e., moieties which are derived from carboxylic acids of the formula RCOOH where R is alkyl, and preferably is lower alkyl. Esters can be reconverted to the free acids, if desired, by using conventional hydrogenolysis or hydrolysis procedures. Amides and prodrugs may also be prepared using techniques known to those skilled in the art or described in the pertinent literature. For example, amides may be prepared from esters, using suitable amine reactants, or they may be prepared from an anhydride or an acid chloride by reaction with ammonia or a lower alkyl amine. Prodrugs are typically prepared by covalent attachment of a moiety which results in a compound that is therapeutically inactive until modified by an individual""s metabolic system. Preferred compounds are in salt form, such as the acid addition (e.g., HCl) salts of sotalol and amiodarone.
Stereoisomers of the active agents are also included as part of the dosage forms described herein. A stereoisomer is a compound having the same molecular weight, chemical composition, and constitution as another, but with the atoms arranged differently. That is, certain identical chemical moieties are at different orientations in space. This difference has the consequence of rotating the plane of polarized light. A pair of stereoisomers that are mirror images of each other are defined as enantiomers. Individual stereoisomers or enantiomers may have unique or beneficial properties that make that individual isomer particularly well-suited for the present invention. Consequently, individual stereoisomers or enantiomers and mixtures thereof of the active agents are included as part of the invention. Thus, each active agent may be present in the formulation as a racemate, i.e., equal amounts of each enantiomer, an enantiomerically pure form, e.g., d-sotalol, l-sotalol, or a mixture of nonequal amounts of each enantiomer, e.g., nonequal amounts of d-sotalol/l-sotalol.
Although any antiarrhythmic agent can be included in the invention, it is preferred that the antiarrhythmic agent is a class II or class III agent. Sotalol is a particularly preferred class II agent while amiodarone is a particularly preferred class III agent for incorporation into the dosage form. Although any form (e.g., salt, base or amide form) may be used, a salt form is preferred when either sotalol or amiodarone is present in the dosage form. It is particularly preferred, however, that sotalol hydrochloride or amiodarone hydrochloride is present in the dosage form of the present invention.
The invention provides pharmaceutical dosage forms that provide the pulsatile delivery of an antiarrhythmic agent. By xe2x80x9cpulsatilexe2x80x9d is meant that a plurality of drug doses are released at spaced apart intervals of time. Generally, upon ingestion of the dosage form, release of the initial dose is substantially immediate, i.e., the first drug release xe2x80x9cpulsexe2x80x9d occurs within about one hour of ingestion. This initial pulse is followed by a first time interval during which very little or no drug is released from the dosage form, after which a second dose is then released. Similarly, a second nearly drug release-free interval between the second and third drug release pulses may be designed. The duration of the nearly drug release-free time interval will vary depending upon the dosage form design e.g., a twice daily dosing profile, a three times daily dosing profile, etc. For dosage forms providing a twice daily dosage profile, the nearly drug release-free interval has a duration of approximately 8 hours to 12 hours between the first and second dose. For dosage forms providing a three times daily profile, the nearly drug release-free interval has a duration of approximately 7 hours to 9 hours between each of the three doses.
In one embodiment, the aforementioned pulsatile release profile is achieved with dosage forms that are closed and preferably sealed capsules housing at least two drug-containing xe2x80x9cdosage unitsxe2x80x9d wherein each dosage unit within the capsule provides a different drug release profile. Control of the delayed release dosage unit(s) is accomplished by a polymer coating of the dosage unit. Each dosage unit may comprise a compressed or molded tablet, wherein each tablet within the capsule provides a different drug release profile. For dosage forms mimicking a twice a day dosing profile, a first tablet releases drug substantially immediately following ingestion of the dosage form, while a second tablet releases drug approximately 6 hours to less than 14 hours following ingestion of the dosage form. For dosage forms mimicking a three times daily dosing profile, a first tablet releases drug substantially immediately following ingestion of the dosage form, a second tablet releases drug approximately 6 hours to less than 14 hours following ingestion of the dosage form, and the third tablet releases drug at least 14 hours to approximately 18 hours following ingestion of the dosage form. It is possible that the dosage form includes more than three tablets. While the dosage form will not generally include more than a third tablet, dosage forms housing more than three tablets are within the scope of the present invention.
Alternatively, each dosage unit in the capsule may comprise a plurality of drug-containing beads, granules or particles. As is known in the art, drug-containing xe2x80x9cbeadsxe2x80x9d refer to beads made with drug and one or more excipients or polymers. Drug-containing beads can be produced by applying drug to an inert support, e.g., inert sugar beads coated with drug or by creating a xe2x80x9ccorexe2x80x9d comprising both drug and one or more excipients. As is also known, drug-containing xe2x80x9cgranulesxe2x80x9d and xe2x80x9cparticlesxe2x80x9d comprise drug particles that may or may not include one or more additional excipients or polymers. In contrast to drug-containing beads, granules and particles do not contain an inert support. Granules generally comprise drug particles and require further processing. Generally, particles are smaller than granules, and are not further processed. Although beads, granules and particles may be formulated to provide immediate release, beads and granules are generally employed to provide delayed release.
For dosage forms mimicking a twice a day dosing profile, a first group beads, granules or particles releases drug substantially immediately following ingestion of the dosage form, while a second group of beads or granules preferably releases drug approximately 8 hours to less than 14 hours following ingestion of the dosage form. For dosage forms mimicking a three times daily dosing profile, a first group of beads, granules or particles releases drug substantially immediately following ingestion of the dosage form, a second group of beads or granules preferably releases drug approximately 6 hours to 10 hours following ingestion of the dosage form, and a third group of beads, granules or particles releases drug at least 14 hours to approximately 18 hours following ingestion of the dosage form. The above-mentioned tablets, beads, granules and particles of different drug release profiles (e.g., immediate and delayed release profiles) may be mixed and included in a capsule to provide a pulsatile dosage form having the desired release profile.
In another embodiment, the individual dosage units are compacted in a single tablet, and may represent integral but discrete segments thereof (e.g., layers), or may be present as a simple admixture. For example, drug-containing beads, granules or particles with different drug release profiles (e.g., immediate and delayed release profiles) can be compressed together into a single tablet using conventional tableting means.
In a further alternative embodiment, a dosage form is provided that comprises an inner drug-containing core and at least one drug-containing layer surrounding the inner core. An outer layer of this dosage form contains an initial, immediate release dose of the drug. For dosage forms mimicking twice daily dosing, the dosage form has an outer layer that releases drug substantially immediately following oral administration and an inner core having a polymeric-coating that preferably releases the active agent approximately 8 hours to less than 14 hours following ingestion of the dosage unit. For dosage forms mimicking three times daily dosing, the dosage form has an outer layer that releases drug substantially immediately following oral administration, an inner core that preferably releases drug at least 14 hours to 18 hours following oral administration and a layer interposed between the inner core and outer layer that preferably releases drug approximately 6 hours to 10 hours following ingestion of the dosage form. The inner core of the dosage form mimicking three times daily dosing may be formulated as compressed delayed release beads or granules.
Alternatively, for dosage forms mimicking three times daily dosing, the dosage form has an outer layer and an inner layer free of drug. The outer layer releases drug substantially immediately following oral administration, and completely surrounds the inner layer. The inner layer surrounds both the second and third doses and preferably prevents release of these doses for approximately 6 hours to 10 hours following oral administration. Once released, the second dose is immediately available while the third dose is formulated as delayed release beads or granules such that release of the third dose is effected approximately 4 hours to 12 thereafter effectively resulting in release of the third dose at least 14 hours to approximately 18 hours following ingestion of the dosage form. The second and third doses may be formulated by admixing immediate release and delayed release beads, granules or particles and compressing the admixture to form a second and third dose-containing core followed by polymeric coating to achieve the desired three times daily dosing profile.
As will be appreciated by those skilled in the art and as described in the pertinent texts and literature, a number of methods are available for preparing drug-containing tablets, beads, granules or particles that provide a variety of drug release profiles. Such methods include, but are not limited to, the following: coating a drug or drug-containing composition with an appropriate coating material, typically although not necessarily a incorporating a polymeric material; increasing drug particle size; placing the drug within a matrix; and forming complexes of the drug with a suitable complexing agent.
The delayed release dosage units in any of the above embodiments can be prepared, for example, by coating a drug or a drug-containing composition with a selected coating material. The drug-containing composition may be, e.g., a tablet for incorporation into a capsule, a tablet for use as an inner core in a xe2x80x9ccoated corexe2x80x9d dosage form, or a plurality of drug-containing beads, particles or granules, for incorporation into either a tablet or capsule. Preferred coating materials are comprised of bioerodible, gradually hydrolyzable, gradually water-soluble, and/or enzymatically degradable polymers, and may be conventional xe2x80x9centericxe2x80x9d polymers. Enteric polymers, as will be appreciated by those skilled in the art, become soluble in the higher pH environment of the lower gastrointestinal tract or slowly erode as the dosage form passes through the gastrointestinal tract, while enzymatically degradable polymers are degraded by bacterial enzymes present in the lower gastrointestinal tract, particularly in the colon. Suitable coating materials for effecting delayed release include, but are not limited to, cellulosic polymers such as hydroxypropyl cellulose, hydroxyethyl cellulose, hydroxymethyl cellulose, hydroxypropyl methyl cellulose, hydroxypropyl methyl cellulose acetate succinate, hydroxypropylmethyl cellulose phthalate, methylcellulose, ethyl cellulose, cellulose acetate, cellulose acetate phthalate, cellulose acetate trimellitate and carboxymethylcellulose sodium; acrylic acid polymers and copolymers, preferably formed from acrylic acid, methacrylic acid, methyl acrylate, ethyl acrylate, methyl methacrylate and/or ethyl methacrylate, and other methacrylic resins that are commercially available under the tradename Eudragit(copyright) (Rohm Pharma; Westerstadt, Germany), including Eudragit(copyright) L30D-55 and L100-55 (soluble at pH 5.5 and above), Eudragit(copyright) L-100 (soluble at pH 6.0 and above), Eudragit(copyright) S (soluble at pH 7.0 and above, as a result of a higher degree of esterification), and Eudragits(copyright) NE, RL and RS (water-insoluble polymers having different degrees of permeability and expandability); vinyl polymers and copolymers such as polyvinyl pyrrolidone, vinyl acetate, vinylacetate phthalate, vinylacetate crotonic acid copolymer, and ethylene-vinyl acetate copolymer; enzymatically degradable polymers such as azo polymers, pectin, chitosan, amylose and guar gum; and shellac. Combinations of different coating materials may also be used. Multi-layer coatings using different polymers may also be applied.
The preferred coating weights for particular coating materials may be readily determined by those skilled in the art by evaluating individual release profiles for tablets, beads and granules prepared with different quantities of various coating materials. Generally, however, a coating weight of approximately 5 wt. % to 50 wt. % is used to achieve an approximately 6 hour to less than 14 hour delay in release of the active agent. Additional amounts of the coating material will provide longer delays in release, e.g., at least a 14 hour to approximately 18 hour delay in release.
The coating composition may include conventional additives, such as plasticizers, pigments, colorants, stabilizing agents, glidants, etc. A plasticizer is normally present to reduce the fragility of the coating, and will generally represent about 10 wt. % to 50 wt. % relative to the dry weight of the polymer. Examples of typical plasticizers are, but not limited to, polyethylene glycol, propylene glycol, triacetin, dimethyl phthalate, diethyl phthalate, dibutyl phthalate, dibutyl sebacate, triethyl citrate, tributyl citrate, triethyl acetyl citrate, castor oil and acetylated monoglycerides. A stabilizing agent is preferably used to stabilize particles in the dispersion. Typical stabilizing agents are nonionic emulsifiers such as sorbitan esters, polysorbates and polyvinylpyrrolidone. Glidants are recommended to reduce sticking effects during film formation and drying, and will generally represent approximately 25 wt. % to 100 wt. % of the polymer weight in the coating solution. One effective glidant is talc. Other glidants such as magnesium stearate and glycerol monostearates may also be used. Pigments such as titanium dioxide may also be used. Small quantities of an anti-foaming agent, such as silicons and simethicone, may also be added to the coating composition.
The delayed release dosage units may be coated with the delayed release polymer coating using conventional techniques, e.g., using a conventional coating pan, an airless spray technique, fluidized bed coating equipment (with or without a Wurster insert), or the like. For detailed information concerning materials, equipment and processes for preparing tablets and delayed release dosage, reference may be made to Pharmaceutical Dosage Forms: Tablets, eds. Lieberman et al. (New York: Marcel Dekker, Inc., 1989), and to Ansel et al., Pharmaceutical Dosage Forms and Drug Delivery Systems, 6th Ed. (Media, PA: Williams and Wilkins, 1995).
Alternatively, a delayed release tablet may be formulated by dispersing the drug within a matrix of a suitable material such a hydrophilic polymer or a fatty compound. The hydrophilic polymers may be comprised of polymers or copolymers of cellulose, cellulose ester, acrylic acid, methacrylic acid, methyl acrylate, ethyl acrylate, and vinyl or enzymatically degradable polymers or copolymers as described above. These hydrophilic polymers are particularly useful for providing a delayed release matrix. Fatty compounds for use as a matrix material include, but are not limited to, waxes (e.g. carnauba wax) and glycerol tristearate. Once the active ingredient is mixed with the matrix material, the mixture can be compressed into tablets.
The immediate release dosage unit of the dosage formxe2x80x94i.e., a tablet, a plurality of drug-containing beads, granules or particles, or an outer layer of a coated core dosage formxe2x80x94contains a therapeutically effective quantity of the active agent with conventional pharmaceutical excipients. The immediate release dosage unit may or may not be coated, and may or may not be admixed with the delayed release dosage unit or units (as in an encapsulated mixture of immediate release drug-containing granules, particles or beads and delayed release drug-containing granules or beads). A preferred method for preparing immediate release tablets (e.g., as incorporated into a capsule) is by compressing a drug-containing blend, e.g., blend of granules, prepared using a direct blend, wet-granulation or dry-granulation process. Immediate release tablets may also be molded rather than compressed, starting with a moist material containing a suitable water-soluble lubricant. However, preferred tablets herein are manufactured using compression rather than molding. A preferred method for forming immediate release drug-containing blend is to mix drug particles directly with one or more excipients such as diluents (or fillers), binders, disintegrants, lubricants, glidants, colorants or the like. As an alternative to direct blending, a drug-containing blend may be prepared by using a wet-granulation or dry-granulation processes. Beads containing the active agent may also be prepared by any one of a number of conventional techniques, typically starting from a fluid dispersion. For example, a typical method for preparing drug-containing beads involves blending the active agent with conventional pharmaceutical excipients such as microcrystalline cellulose, starch, polyvinylpyrrolidone, methyl cellulose, talc, metallic stearates, silicone dioxide, or the like. The admixture is used to coat a bead core such as a sugar sphere (or so-called xe2x80x9cnon-pareilxe2x80x9d) having a size of approximately 20 to 60 mesh.
An alternative procedure for preparing drug beads is by blending drug with one or more pharmaceutically acceptable excipients, such as microcrystalline cellulose, lactose, cellulose, polyvinyl pyrrolidone, talc, magnesium stearate, a disintegrant, etc., extruding the blend, spheronizing the extrudate, drying and optionally coating to form the immediate release beads.
Optional pharmaceutically acceptable excipients present in the drug-containing tablets, beads, granules or particles include, but are not limited to, diluents, binders, lubricants, disintegrants, colorants, stabilizers, surfactants and the like. Diluents, also termed xe2x80x9cfillers,xe2x80x9d are typically necessary to increase the bulk of a solid dosage form so that a practical size is provided for compression of tablets or formation of beads and granules. Suitable diluents include, for example, dicalcium phosphate dihydrate, calcium sulfate, lactose, sucrose, mannitol, sorbitol, cellulose, microcrystalline cellulose, kaolin, sodium chloride, dry starch, hydrolyzed starches, pregelatinized starch, silicone dioxide, titanium oxide, magnesium aluminum silicate and powder sugar. Binders are used to impart cohesive qualities to a solid dosage formulation, and thus ensure that a tablet or bead or granule remains intact after the formation of the dosage forms. Suitable binder materials include, but are not limited to, starch, pregelatinized starch, gelatin, sugars (including sucrose, glucose, dextrose, lactose and sorbitol), polyethylene glycol, waxes, natural and synthetic gums such as acacia, tragacanth, sodium alginate, cellulose and veegum, and synthetic polymers such as acrylic acid and methacrylic acid copolymers, methacrylic acid copolymers, methyl methacrylate copolymers, aminoalkyl methacrylate copolymers, polyacrylic acid/polymethacrylic acid and polyvinylpyrrolidone. Lubricants are used to facilitate tablet manufacture; examples of suitable lubricants include, for example, magnesium stearate, calcium stearate, stearic acid, glycerol behenate, and polyethylene glycol, talc, and mineral oil. Disintegrants are used to facilitate dosage form disintegration or xe2x80x9cbreakupxe2x80x9d after administration, and are generally starch, sodium starch glycolate, sodium carboxymethyl starch, sodium carboxymethylcellulose, hydroxypropyl cellulose, pregelatinized starch, clays, cellulose, alginine, gums or cross linked polymers, such as cross-linked PVP (Polyplasdone XL from GAF Chemical Corp). Stabilizers are used to inhibit or retard drug decomposition reactions which include, by way or example, oxidative reactions. Surfactants may be anionic, cationic, amphoteric or nonionic surface active agents. Suitable anionic surfactants include, but not limited to those containing carboxylate, sulfonate and sulfate ions. Examples for anionic surfactants are sodium, potassium, ammonium of long chain alkyl sulfonates and alkyl aryl sulfonates such as sodium dodecylbenzene sulfonate; dialkyl sodium sulfosuccinates, such as sodium dodecylbenzene sulfonate; dialkyl sodium sulfosuccinates, such as sodium bis-(2-ethylthioxyl)-sulfosuccinate; and alkyl sulfates such as sodium lauryl sulfate. Cationic surfactants include, but not limited quaternary ammonium compounds such as benzalkonium chloride, benzethonium chloride, cetrimonium bromide, stearyl dimethylbenzyl ammonium chloride, polyoxyethylene (15) and coconut amine. Examples for nonionic surfactants are, but not limited to, ethylene glycol monostearate, propylene glycol myristate, glyceryl monostearate, glyceryl stearate, polyglyceryl-4-oleate, sorbitan acylate, sucrose acylate, PEG-150 laurate, PEG-400 monolaurate, polyoxyethylene (8) monolaurate, polysorbates, polyoxyethylene (9) octylphenylether, PEG-1000 cetyl ether, polyoxyethylene (3) tridecyl ether, polypropylene glycol (18) butyl ether, Poloxamer 401, stearoyl monoisopropanolamide, and polyoxyethylene (5) hydrogenated tallow amide. Examples for amphoteric surfactants are, but not limited to, sodium N-dodecyl-xcex2-alanine, sodium N-lauryl-xcex2-iminodipropionate, myristoamphoacetate, lauryl betaine and lauryl sulfobetaine. If desired, the tablets, beads granules or particles may also contain minor amount of nontoxic auxiliary substances such as wetting or emulsifying agents, pH buffering agents, preservatives, and the like.
The amount of active agent released in each dose will be a therapeutically effective amount, and will depend upon the dosage form itself (e.g., a dosage form having a twice daily dosing profile). When sotalol is included in the dosage form, the total amount of sotalol or a pharmaceutically acceptable salt thereof (e.g., the hydrochloride salt) in the dosage unit is in the range of approximately 50 mg to 700 mg, preferably 80 mg to 640 mg. When amiodarone is included in the dosage form, the total amount of amiodarone or a pharmaceutically acceptable salt thereof (e.g., the hydrochloride salt) in the dosage unit is in the range of approximately 200 mg to 1000 mg, preferably 400 mg to 800 mg.
Typically, the total amount of active agent in a dosage form is divided evenly between each pulse contained in the dosage form. For dosage forms that mimic a twice a day profile, the active agent in immediate release form generally represents about 30 wt. % to 70 wt. %, preferably 40 wt. % to 60 wt. %, of the total active agent in one dosage form, while, correspondingly, the active agent in the delayed release form generally represents about 70 wt. % to 30 wt. %,: preferably 60 wt. % to 40 wt. %, of the total active agent in one dosage form. Similarly, for dosage forms that mimic three times daily dosing profile, the active agent in the immediate release unit(s) and in each of the two delayed release units represents about 20 wt. % to 50 wt. %, preferably 25 wt. % to 40 wt. %, of the total active agent in one dosage form.
For dosage forms containing sotalol and mimicking a twice daily dosing profile, the immediate release dosage unit in each dosage form typically contains approximately 25 mg to 350 mg, preferably 40 mg to 320 mg, of sotalol while the delayed release dosage unit contains approximately 25 mg to 350, preferably 40 mg to 320 mg, of the active agent. For dosing forms containing amiodarone and mimicking a twice daily dosing profile, the immediate release dosage unit in each dosage form typically contains approximately 100 mg to 300 mg, preferably 200 mg, of amiodarone while the delayed release dosage unit contains approximately 100 mg to 300 mg, preferably 200 mg, of the active agent.
For dosage forms containing sotalol and mimicking a three times daily dosing profile, the immediate release dosage unit in each dosage form typically contains approximately 16 mg to 233 mg, preferably 26 mg to 214 mg, of sotalol while each of the delayed release dosage units contain approximately 16 mg to 233 mg, preferably 26 mg to 214 mg, of the active agent. For dosing forms containing amiodarone and mimicking a three times daily dosing profile, the immediate release dosage unit and first delayed release dosage unit in each dosage form typically contain approximately 100 mg to 300 mg, preferably 200 mg, of amiodarone while the second delayed release dosage unit contains approximately 100 mg to 200 mg of the active agent.
The invention also includes a method for treating an individual suffering from a cardiac arrhythmia comprising orally administering a dosage form of the invention preferably, although not necessarily, once daily. Typically the dosage forms are employed to treat individuals suffering from atrial fibrillation, atrial flutter, supra ventricular arrhythmia, ventricular tachycardia (including sustained ventricular tachycardia) and ventricular arrhythmia. By providing pulsatile release of the active agent, the dosage forms of the invention minimize the development of tolerance (and thereby loss of efficacy) due to supersensitization of the cardioreceptors.
Experimental
The practice of the present invention will employ, unless otherwise indicated, conventional techniques of pharmaceutical formulation, medicinal chemistry, biological testing, and the like, which are within the skill of the art. Such techniques are explained fully in the literature. Preparation of various types of pharmaceutical formulations are described, for example, in Lieberman et al., cited supra; synthesis of chiral drugs is described, inter alia, in Wilson and Grisvold, Textbook of Organic, Medicinal and Pharmaceutical Chemistry (Lippincott-Raven Publishers, 1991); and Gibaldi and Perrier, Pharmacokinetics (Marcel Dekker, 1982), provides a description of the biological testing procedures useful to evaluate compounds such as those described and claimed herein. All patents, patent applications and publications mentioned herein, both supra and infra, are hereby incorporated by reference.